The love-hate of water and coffee brewing: Part two

Espresso

Depending on the condition of the tap water and the customer’s price point, there are typically two treatment paths you can go for espresso brewing: Ion exchange or reverse osmosis (or both). Ion exchange can be a small under-counter brine softener, which is paired with a carbon filter to remove chlorine for taste and odor. This can be the most inexpensive option. The drawback of course is the customer has to be diligent about adding the salt. Another option is to use a rechargeable resin tank system, which is popular in Europe. Some of these systems have carbon block or GAC integrated into the tank for chlorine removal. These systems require some logistics to retrieve the tanks and recharge them.

A third option is to use a POU quick change system that uses WAC. When the resin expires, the cartridge is simply replaced with a new one. Like the rechargeable systems, these include carbon block or GAC, and they also typically have a pre-filter as well for larger particulate (10-plus micron). These systems are designed to specifically target the four essential water parameters at once, which are hardness, alkalinity, pH and TDS. Scale minerals are removed and exchanged for hydrogen instead of sodium as in a sodium softener. The added hydrogen converts the alkalinity — carbonates to H₂O and CO₂, which is then released as a gas. This results in a lower TDS, lower alkalinity, lower total hardness and lower pH, to the optimal water specification. Some of these systems have a fixed bypass, which blends about 20 percent of filtered water with the softened water. This provides two functions: To create a buffer so the water doesn’t become too acidic, and to keep enough mineral in the water for good extraction of the oils and good flavor of the coffee beverage.

The newest models take this a step further by offering the customer the ability to tailor the hardness to a specific water recipe. The problem with fixed bypass systems is that they produce final product water that is determined by the volume of mineral in the source water. In other words, the customer has no control over how much mineral gets blended, so if the incoming water has very high hardness, the product water could finish with much higher mineral content than is necessary, resulting in poor quality beverages and scale risk on the machine. These new systems provide an adjustable bypass, so the blend can be set to reach a preferred hardness (100 ppm), regardless of the total hardness of the incoming water (as long as the water starts with enough mineral). This is a significant new feature for baristas who don’t want to go to the expense of reverse osmosis.

The drawback to these quick change softening systems is that the expiration is not evident, unlike a typical carbon and polyphosphate system where pressure drop or reduced flow indicates it’s time to change the filter. This can easily be managed by using a flow meter, or just calculating the life expectancy of the filter using the carbonate hardness in the inlet water and capacity charts.

It’s also worth noting that system performance can’t be measured by the total hardness of the product water, since the system impacts the four parameters responsible for scale buildup. A quick test on performance is to measure the TDS on the incoming and outgoing water. If the difference is still in proportion to the setting, the system is still active. To measure the filter’s effectiveness carbonate hardness should be tested, not calcium hardness using a typical hardness test strip. This can easily be done using an inexpensive titration test for carbonate hardness.

Reverse osmosis provides some benefits over ion exchange. Depending on the system and how it’s set up, it removes 96-99 percent of TDS and hardness, including heavy metals, chloride, iron, lead, nitrate, sulfate and even chromium-6. Many RO systems also integrate a pre-filter and carbon filter since chlorine is damaging to RO membranes. In addition some systems have blending capabilities that allow for customizing the TDS and for multiple water outputs. Reverse osmosis also provides consistency, so for specialty coffee chains it ensures the coffee beverages are brewed with the same water quality across all locations. This is also a technology that can be applied to both espresso and drip coffee brewing, whereas salt softening is not a good technology for drip coffee. This is explained later.

The drawbacks to RO include the higher upfront cost versus POU filtration and softening, the necessity of power (unless the system is driven by permeate only, no electric pump) and a drain, the need for a floor tank and the high water waste. Some of the newer RO systems are significantly more efficient at reducing wastewater and some even have on-board tanks to save space.

Being able to blend filtered water with the pure RO product water is very beneficial because pure RO water can cause over extraction of the coffee grounds. The blending retains some mineral to prevent this, and the mineral adds flavor. Pure RO water can also cause corrosion on metals in the brewer. Some RO systems have a blending capability, but if not it can be retrofitted in the field.

If a softener is already present at the location, some installers will use a portion of the softened water to feed the RO, which reduces scaling of the RO membrane and increases its life.

Drip coffee

The most common water treatment for drip brewing is a carbon filter with a scale inhibitor. These provide a cost effective means of removing chemicals and particulate and preventing scale on the equipment.

The scale inhibitor is usually polyphosphate. This was originally developed as water-based lubricants or corrosion inhibitors, but it was discovered that they could also slow the scale development process when added to the water supply in very small amounts. Polyphosphates interfere with the bonding process of the mineral components, or the cations and anions, of scale. The minerals are kept in suspension and flushed through the system instead of binding together to form scale. Polyphosphates offer a reasonable, low-cost compromise for scale reduction when compared to more complex technologies, such as water softening and reverse osmosis. They are reasonably effective in water supplies with hardness levels up to 15 gpg. Above this, alternative methods of scale control should be considered. Sometimes orthophosphates are added as well to provide buffering so the water doesn’t become acidic and "aggressive" on metals.

There are generally two disadvantages to these types of filters. The first is that it adds polyphosphate to the water and even though this is food grade and tasteless, some "purists" want nothing added. The second is that it does not change TDS, hardness, pH and alkalinity. Polyphosphates do not perform well in espresso brewing because of the higher temperatures used and the pressures.

Ion exchange systems that use salt are not recommended for drip coffee brewing. Sodium carbonate as a result of the softening causes coffee grounds to swell and extends the extraction time which can result in over extraction. If too much oil is released, especially bitter oils, it can result in a bitter coffee and often an "oil slick" on the surface of the coffee. Sodium softened water is not ok for espresso either.

However, the WAC ion exchange systems will work for drip coffee. The reason is that, as described above, they don’t add sodium to the water. But, in the past, these types of systems didn’t have the capacity to keep up with the much higher volumes of drip brewing (espresso brewing uses only about four ounces of water per shot), so frequent change outs would be required. Today, though, there are POU WAC softening systems that have enough capacity for pot brewing.

One last note on treating water for coffee and espresso: In parts of the world where mineral content is naturally low, such as Seattle and many of the Asia Pacific countries, dissolved mineral must be added. A calcite feed cartridge can be installed to elevate the calcium hardness. This is paired with carbon filtration for taste and odor.

Baristas and specialty coffee shop owners understand the importance of quality water for brewing, but they don’t always know the best ways to treat it. That’s why most baristas and owners that I’ve met appreciate consultative help from a water treatment specialist, especially one who speaks their "lingo." And today, there are some excellent products available, including POU ion exchange systems that provide tailored hardness and high efficient RO systems with blending.

Roy E. Parker is the senior marketing manager for Pentair Foodservice, which includes the brands Everpure and SHURflo. He’s been with Pentair for five years and has helped to launch new products, including the Claris softening and filtration systems and the award winning MRS 600 HE and HE II high efficiency reverse osmosis systems, and new tools, such as the SMARTWORKS™ and SMART OFFICE WATER interactive water testing and analysis programs.